Lizardfang (5e Feat)
From D&D Wiki
You have mastered the arts of cooperated and somewhat dirty tactics. You gain the following benefits.
- Whenever an allied creature attacks a creature within 5 ft of you, you may use your reaction to attack them. This attack is made with a -4 penalty to attack rolls.
- Whenever you have disadvantage on a melee attack roll you make, you may use your reaction to gain a +4 bonus to attack roll of that attack.